The Flow Boiling Crisis of Saturated Water in Pipes at High Pressures

The procedures developed by the authors for calculating the distribution of the liquid over the channel cross section in the dispersed-annular flows open up opportunities for more justified modeling of the conditions for the occurrence of a boiling crisis at positive values of the relative enthalpy (quality) of the flow. However, a comparison of the calculated values of the liquid flowrate in the film with the recommended values of critical heat flux (CHF) in water flow boiling in pipes has demonstrated that, in general, there is no obvious correlation between them. An analysis confirms the well-known opinion that a unified model of the flow boiling crisis in pipes cannot be constructed. At the same time, the regularities revealed in calculating the entrainment and deposition of droplets should be considered in developing a crisis model. An increase in CHF with mass flowrate, which was discovered experimentally and accounted for in the reference tables in a wide range of high pressures and mass flowrates, gives us reasons to return to Doroshchuk’s hypothesis about the “deposition crisis.” Application of the correlation for the droplet deposition rate in a disperse-annular flow enabled us to quantitatively verify this correlation. The predictions obtained using this correlation agree well with the tabulated data at a flow quality from 0.15 to 0.40 and mass flowrates above 2000 kg/(m² s). At the same time, it has been demonstrated that the widespread use of extrapolation of the CHF values recommended in the latest edition of these tables makes them, in fact, not only unreliable but also physically unjustified in a certain range of parameters. This paper identifies several such ranges wherein revision of the tables is essential.